Recently, for example, systems in which a plurality of AV apparatuses are connected via a digital interface at homes for transmitting and recording digital data such as music information, video information or the like are becoming popular.
For example, in an apparatus such as a video camera, a DVD player or the like having an interface of the IEEE (Institute of Electrical and Electronics Engineers) 1394 high-performance serial bus (hereinafter simply referred to as the IEEE 1394 serial bus), since data can be recorded with high fidelity, it is necessary to prevent data from being illegally copied.
For example, a key is stored indicating whether or not recording of movie information onto a magneto-optical disc apparatus is permitted, and by using this key, authentication is performed as to whether the magneto-optical disc apparatus is an authorized apparatus, that is, an apparatus which has received a license from the copyright holder. Thus, recording of the movie information onto only a magneto-optical disc apparatus which is authenticated as an authorized unit is permitted. In such a case, it is necessary to perform authentication of the counterpart apparatus between an apparatus on the side which transmits movie information (hereinafter referred to as a source) and an apparatus on the side which receives the transmission (hereinafter referred to as a sink).
For the purpose of protecting copyright in such a system, various authentication methods have been proposed. For an authentication protocol used for these authentication methods, an encryption algorithm is often used.
Meanwhile, when transmitting music data between apparatuses, for example, if transmission is stopped during the transmission of the music data or if the quantity of data which can be transmitted is extremely reduced, it becomes impossible for the receiving side to obtain data required for playback and the music might be interrupted. Therefore, it is necessary to transmit music data in a state where a band of a certain extent is secured.
On the other hand, when transmitting information which is not music data itself but is related to music data, for example, lyrics, a photograph of an artist or the like, the real-time property is not required in comparison with the case of transmitting the music data itself. Therefore, it is possible to transmit the information by using a transmission method in which a transmission band is not secured. In general, it is often desired to use the transmission method in which a transmission band is not secured, because the band of the entire transmission line is not used.